Fix an analyzer error in http and barback.

pkg/http/lib/src/utils.dart

Index: pkg/http/lib/src/utils.dart
diff --git a/pkg/http/lib/src/utils.dart b/pkg/http/lib/src/utils.dart
index 64c50c4269e0c0e9c6a09701c0f1ec7465811625..3420a2e3b120814fbc56ff4defc87b2862586989 100644
--- a/pkg/http/lib/src/utils.dart
+++ b/pkg/http/lib/src/utils.dart
@@ -112,7 +112,9 @@ bool isPlainAscii(String string) => _ASCII_ONLY.hasMatch(string);
 /// If [input] is a [TypedData], this just returns a view on [input].
 Uint8List toUint8List(List<int> input) {
   if (input is Uint8List) return input;
-  if (input is TypedData) return new Uint8List.view(input.buffer);
+  if (input is TypedData) {
+    return new Uint8List.view((input as TypedData).buffer);
+  }
   return new Uint8List.fromList(input);
 }